1. Technical Field
The invention disclosed is broadly related to digital circuits and more particularly is directed to an improved technique for generating data clock waveforms.
2. Background Art
A common problem in decoding asynchronous serial data in communications links is that of reconstructing the original transmission clock for use in decoding the serial data stream. The most efficient serial coding schemes (i.e. NON-RETURN-TO-ZERO and its derivatives) are not self-clocking (do not contain the clock timing information in the data stream). A common approach in prior art is to utilize a voltage or current controlled oscillator as the reconstructed clock and to "phase lock" this oscillator to the incoming data stream via feedback from a phase comparison between the reconstructed clock and the incoming data. The disadvantages to this approach are that it takes a finite time to achieve "phase lock," a unique signature must be transmitted and decoded to indicate the "real" beginning of data, and clock timing can never be exact as some phase difference is necessary to maintain the error signal which tunes the oscillator.